The overall aim of this program is to develop models for enzyme replacement therapy and lysosomal storage diseases and to test the efficacy of enzyme replacement in deficient human subjects. In project I, animal models will be studied to: 1) define the distribution of receptors which mediate endocytosis of natural and chemically modified forms of human beta-glucuronidase, 2) study the clearance and fate of beta-glucuronidase covalently linked to ligands with affinity for cobalamin carrier proteins and low density lipoprotein, and 3) study enzyme uptake by the central nervous system. Cell culture studies will be done to: 1) identify the fibroblast pinocytosis receptor for high-uptake enzyme, 2) study enzyme uptake by isolated neurons and other cells from brain and peripheral nerves, and 3) characterize membrane abnormalities in I-cell fibroblasts. Biochemical studies will be done to: 1) characterize the high-uptake component on high-uptake forms of lysosomal enzymes, 2) study the abnormality of I-cell secretion enzymes, and 3) identify the membrane receptors which mediate uptake of lysosomal enzymes. Results of these studies will guide clinical trials at enzyme replacement in beta-glucuronidase deficient patients. In Project III, the goals are: 1) purification and modification of beta-glucuronidase from human placenta and human spleen for use in animal studies, clinical trials, and structural studies, and 2) correlation of structural differences between native and modified forms of human beta-glucuronidase with its catalytic and recognition functions. In Project V, the goals are to identify the pinocytosis receptors responsible for recognition and uptake of lysosomal enzymes, to characterize the uptake systems in whole cells, and to isolate receptors and study their binding properties in vitro.